Formation And Properties Of Fe/Ni And Fe/Co Binary Alloy Nanowires

One-dimensional (1-D) nanostructure materials such as nanowires with large magnetic anisotropy, squareness ratio and coercivity have attracted much attention due to the potential applications in ultra-high density vertical magnetic recording. The highly ordered anodic aluminum oxide (AAO) template was widely used for assembling 1-D nanostructure materials because of its uniform and nearly parallel porous structures. The AAO templates were prepared by two-step anodic oxidation, Fe/Ni and Fe/Co binary alloy nanowires were deposited into nanoporous alumina by DC and AC electrodeposition respectively. Atomic force microscope (AFM) was used to investigate the morphology of the AAO templates; scanning electron microscope (SEM) and transmission electron microscope (TEM) were were used to investigate the morphology of nanowires; the structure of the nanowire arrays with the AAO templates was obtained with X-ray diffractometer (XRD); the magnetic properties of nanowires embedded within the templates were measured by superconducting quantum interference device magnetometer (SQUID). The main contents as following:1. The AAO templates were prepared by two-step anodic oxidation in H3PO4 and C2H2O4 electrolyte. The uniform pore size and smooth inside wall of holes can be observed in C2H2O4 as well as the pore diameters are about 70 nm. While the channel in the AAO templates synthesized in H3PO4 divaricate easily with the pore diameters are about 150 nm. We prepared AAO templates by two-step anodic oxidation in C2H2O4 electrolyte for assembling nanowires by DC and AC electrodeposition. The phase structures of the templates is amorphous obtained with XRD.2. Fe/Ni binary alloy nanowires were deposited into nanoporous alumina by DC electrodeposition. XRD pattern indicates that all the nanowires have the same microstructure, and the crystallites structure of nanowires are face-center-cubic (fcc) with existence of strong [111] orientation along the nanowire axes. The magnetic properties of nanowires measured by SQUID changed with changing the deposition voltage. It can be seen that the magnetic easy-axis aligned parallel to the wires. It can be seen that the maximum coercivity of 731 Oe and squareness ratio of 0.61 were observed when the deposition voltage was -1.0 V. By comparing the average grain size of nanowires with the single domain particles, we can explain the changes of coercivity.3. Arrays of Co and Fe/Co binary alloy nanowires were fabricated into the AAO template pores by AC electrodeposition. It can be seen that the nanowires electrodeposited in the alumina templates are highly ordered. The nanowires deposited in AAO template are found to be about 50 nm in diameter and 3μm in length. The XRD pattern indicates that the crystallites structure of Co nanowires is hcp with existence of strong [100] orientation along the nanowire axes. While the crystallites structure of Fe-Co binary alloy nanowires is bcc with existence of strong [110] orientation along the nanowire axes. The peaks shift toward to the higher angle when the Co content of nanowires was increased. The uniaxial anisotropy was shown by magnetization hysteresis loops, and the magnetic easy-axis aligned parallel to the wires. With increasing Co content, the coercivity of the nanowire arrays unchanged. Once the Fe/Co nanowires have a high aspect ratio (n>20), the behavior is interpreted using a magnetization reversal model based on"chains of spheres". Compared with the Co nanowires, the Fe/Co binary alloy nanowires have a larger coercive force and squareness ratio. The magnetic domains of nanowires were observed by MFM, and the domains consisted of the light and shade regions of different areas.